The present invention relates generally to magnetoresistive read sensors for use in magnetic read heads. In particular, the present invention relates to a current perpendicular to plane (CPP) spin valve head with reduced side reading and improved magnetic stability.
A magnetic read head retrieves magnetically-encoded information that is stored on a magnetic medium or disc. The magnetic read head is typically formed of several layers that include a top shield, a bottom shield, and a read sensor positioned between the top and bottom shields. The read sensor is generally a type of magnetoresistive sensor, such as a giant magnetoresistive (GMR) read sensor. The resistance of a GMR read sensor fluctuates in response to a magnetic field emanating from a magnetic medium when the GMR read sensor is used in a magnetic read head and positioned near the magnetic medium. By providing a sense current through the GMR read sensor, the resistance of the GMR read sensor can be measured and used by external circuitry to decipher the information stored on the magnetic medium.
A common GMR read sensor configuration is the GMR spin valve configuration in which the GMR read sensor is a multi-layered structure formed of a ferromagnetic free layer, a ferromagnetic pinned layer and a nonmagnetic spacer layer positioned between the free layer and the pinned layer. The magnetization direction of the pinned layer is fixed in a predetermined direction, generally normal to an air bearing surface of the GMR spin valve, while a magnetization direction of the free layer rotates freely in response to an external magnetic field. An easy axis of the free layer is generally set normal to the magnetization direction of the pinned layer. The resistance of the GMR read sensor varies as a function of an angle formed between the magnetization direction of the free layer and the magnetization direction of the pinned layer. This multi-layered spin valve configuration allows for a more pronounced magnetoresistive effect than is possible with anisotropic magnetoresistive (AMR) read sensors, which generally consist of a single ferromagnetic layer.
Typically, the magnetization of the pinned layer is fixed in the predetermined direction by exchange coupling an antiferromagnetic layer to the pinned layer. The antiferromagnetic layer is positioned upon the pinned layer such that the antiferromagnetic layer and the free layer form distal edges of the GMR spin valve. The spin valve is then heated to a temperature greater than a Nxc3xa9el temperature of the antiferromagnetic layer. Next, a magnetic field oriented in the predetermined direction is applied to the spin valve, thereby causing the magnetization direction of the pinned layer to orient in the direction of the applied magnetic field. The magnetic field may be applied to the spin valve before the spin valve is heated to the temperature greater than the Nxc3xa9el temperature of the antiferromagnetic layer. While continuing to apply the magnetic field, the spin valve is cooled to a temperature lower than the Nxc3xa9el temperature of the antiferromagnetic layer. Once the magnetic field is removed from the spin valve, the magnetization direction of the pinned layer will remain fixed, as a result of the exchange with the antiferromagnetic layer, so long as the temperature of the spin valve remains lower than the Nxc3xa9el temperature of the antiferromagnetic layer.
The free layer of a spin valve sensor must be stabilized against the formation of edge domain walls because domain wall motion results in electrical noise, which makes data recovery impossible. A common way to achieve stabilization is with a permanent magnet abutted junction design. Permanent magnets have a high coercive field (i.e., are hard magnets). The field from the permanent magnets stabilizes the free layer and prevents edge domain formation, and provides proper bias.
However, there are several problems with permanent magnet abutted junctions. To properly stabilize the free layer, the permanent magnets must provide more flux than can be closed by the free layer. This undesirable extra flux stiffens the edges of the free layer so that the edges cannot rotate in response to flux from the media, and may also cause shield saturation which adversely affects the ability of the sensor to read high data densities. The extra flux from the permanent magnets may produce multiple domains in the free layer and may also produce dead regions which reduce the sensitivity of the sensor. For very small sensors, which are needed for high density recording, the permanent magnet bias severely reduces the sensitivity of the free layer.
Tabs of antiferromagnetic material or xe2x80x9cexchange tabsxe2x80x9d have also been used to stabilize the free layer of magnetic sensors. Exchange tabs are deposited upon the outer regions of the free layer and are exchange coupled thereto. Functions of the exchange tabs include pinning the magnetization of the outer regions of the free layer in the proper direction, preventing the formation of edge domains and defining the width of an active area of the free layer by preventing free layer rotation at the outer regions of the free layer.
Additional stabilization techniques are desirable, particular for ultra high density heads with small sensors. For 100 Gbit/in2 and beyond magnetic recording storage, the track and linear densities are both very demanding. A typical design for a 100 Gbit/in2 head should have a linear density of about 700 kilobits per inch (KBPI) and a track density of about 145 kilotracks per inch (KTPI). The written track cell for such a head is about 1,000 angstroms by 250 angstroms (i.e., an aspect ratio of about 4). High linear density requires a narrow shield-to-shield spacing. In order to meet the track density requirement, a small sensor size is needed (e.g., 0.1 by 0.1 micrometers). A larger sensor will produce side readings from adjacent tracks.
A novel design is needed to deal with such ultra-high density recording, while maintaining a stable free layer dynamic response and good cross-track characteristics.
A spin valve head according to the present invention includes a spin valve stack having a free layer, a first spacer layer, a pinned layer and a pinning layer. The spin valve stack is configured to operate in a current perpendicular to plane (CPP) mode, wherein a sense current flows substantially perpendicular to a longitudinal plane of the first spacer layer. The spin valve head includes a first shield and a second shield coupled to opposing sides of the spin valve stack. The first and the second shields act as electrodes to couple the sense current to the spin valve stack. The first shield has a concave shape and substantially surrounds the free layer. The spin valve head also includes a second spacer layer and a layer of antiferromagnetic material. The second spacer layer is formed on the free layer. The layer of antiferromagnetic material is formed on the second spacer layer.
The spin valve head of the present invention senses ultra-high density recording, while maintaining a stable free layer dynamic response and good cross-track characteristics. The need for permanent magnet bias is eliminated, allowing a small sensor to be used to meet high track density requirements. The concave wrapped shield configuration reduces the side reading of the head.
FIG. 1 is a cross-sectional view of a magnetic read/write head and magnetic disc taken along a plane normal to an air bearing surface of the read/write head.
FIG. 2 is a layer diagram of an air bearing surface of a magnetic read/write head.
FIG. 3 is a perspective view of a prior art GMR stack.
FIG. 4 is a perspective view of a prior art GMR spin valve stack with permanent magnet abutted junctions.
FIG. 5A shows an ABS view of a CPP type of spin valve according to the present invention.
FIG. 5B shows a cross-sectional view of a CPP type of spin valve according to the present invention.
FIG. 6A shows an ABS view of a second embodiment of a CPP type of spin valve according to the present invention, which provides additional shielding of the free layer.
FIG. 6B shows a cross-sectional view of a second embodiment of a CPP type of spin valve according to the present invention, which provides additional shielding of the free layer.
FIG. 7 shows typical M-H loops of an exchange biased NiFe free layer with a structure NiFe/Cu(10 xc3x85)/IrMn.
FIG. 8 shows a graph of GMR, R and dR versus thickness of a Cu spacer layer in a spin valve with IrMn free layer stabilization.
FIG. 9 shows a graph of interlayer coupling (H1) and effective Hk for a spin valve with IrMn free layer stabilization.
FIG. 10 shows a graph of R and dR versus hard axis field for a spin valve with IrMn free layer stabilization.